Numerous improvements on parachute canopies were made during the last years which lead to better performance of the parachute with respect to its guiding behaviour and the ease of handling such as the provision of guiding windows and other guiding means. These improvements have significantly increased the security during the descending phase as well as the exactness of landing. However, the opening phase of the canopy is still a weak point which is open for improvement.
The opening operation of known hemispherical parachutes comprises inflation of the canopy by air entering at and deviated by the skirt portion of the canopy, which air firstly inflates the superior portion of the canopy, then its center portion and finally its portion adjacent the skirt portion, Problems may arise during several phases of the inflation. First, during the opening of the skirt portion due to the fact that at the considered relative speed between the parachute and the air,considerable and dangerous forces, created by the pressure of the air against the skirt portion, cause severe flapping of the latter during which the skirt portion has the tendency of alternatingly carrying out opening and closing movements. It is very important to restrict the duration of this flapping phase and to assure that it finally ends with the opening of the canopy. Secondly, subsequent to the opening of the skirt portion and the beginning of the inflation of the canopy, opeation problems may arise. Two principal types of malfunctioning are known, one being the appearance of a double dome or a partial inversion and the other, the formation of a pear-like body which may be formed at high speed whereby the canopy is not entirely inflated, constituting an equilibrium between internal and external pressures on either side of the canopy which, herewith, maintains the shape of a pear.
French Pat. No. 1,418,752 provides escape channels for the air arranged at the superior half portion of the canopy in addition to the central channel. The objective thereof is a smoothing of the shock during opening of the canopy and the increase of stability thereof. At the same time these improvements lead to increased security for the opening, as the air entering the canopy in counter current inflates the peak portion of the canopy and disrupts the eventual equilibrium between the internal and external pressures, thereby assuring total inflation. This solution , however, does not increase the inflation speed, does not inhibit the flapping of the skirt portion and relates particularly to the braking before the complete opening of the parachute canopy.
Further, U.S. Pat. No. 2,929,588 proposes to uniformly dispose slots between overlapping trapezoidal gore portions in an annular pattern over the entire canopy, such that the dome, once inflated, represents a perfect hemispherical body, rather than a flat ellipsoid. Such canopies also permit to smooth the opening shock, one of the objectives of the above patent, and to provide the parachute with a positive opening tendency. However this type of canopy does not primarily emphasize the function of the skirt portion since air may pass through all slots simultaneously and without preference. On the other hand, a substantial inconvenience arises from the slots themselves as they are arranged in side-by-side relationship such that they do not provide any directional effect.
U.S. Pat. No. 3,393,885 provides a means permitting control of the air flow through channels such as described in the above French patent. Cross straps are uniformly arranged across the channels, the lengths of these cross straps being substantially identical across the channels. These cross straps connect the superior edge of the channel to the canopy, in particular to the gore portion which supports this channel. The efflux of air is thus guided through a rectangular opening and not anymore through a sickle-shaped slot. Thererefore, differential speed distributions across the opening are inhibited and the efflux approaches the laminar model. These rectangular openings provide a reliable effect during the phase subsequent to inflation, whereby during the inflation the cross straps also prohibit inversion of the canopy, but they do not necessarily contribute to the speed and security of inflation or to the positive opening tendency.
In the following description the term "air entry" is employed to designate a volume within which the air effects a positive effort with respect to the opening of the canopy during which said air is compressed (RAM AIR). The term "air entry" should not be understood in the common meaning designating the section of an air passage only.